Biology subjects

Harter, K. J. W.

Publications and source records attributed to Harter, K. J. W..

5 recordsLinked to original sources

bioRxiv2026

Distinct nanoscale dynamics of growth receptor complexes link hormone perception to rapid cell wall remodeling

Cell elongation is a fundamental process allowing plants to change size and shape, a process governed by several growth promoting hormones. While hormones such as brassinosteroids (BRs) and phytosulfokines (PSKs) have been shown to play important roles in elongation growth, the early steps of signal perception remains elusive, especially with regard to PSK. Here we report a rapid mechanism by which PSK alter cell wall mechanical properties in elongating hypocotyls. Notably, this mode of action differs from that of BR. Making use of atomic force microscopy and fluorescence lifetime imaging microscopy we demonstrate how hallmarks of growing plant cells such as mechanical wall properties, porosity and apoplastic pH are differentially affected by PSK compared to BR. Using super-resolution microscopy, we show that the receptor complex components for BR and PSK display individual spatiotemporal movement and organization patterns. The BR receptor BRI1 transitions to a faster diffusive state upon ligand perception, while the PSK receptor PSKR1 associates in tighter clusters. The shared co-receptor BAK1 displays a selective decrease in cluster density after PSK treatment. We found that the putative cell wall state sensor RLP44 is required for the observed changes, however the spatiotemporal dynamics of RLP44 are not altered during signaling. We propose a model of how cell walls are specifically tuned by BRI1- and PSKR1-centered signaling hubs as potential prerequisites for and during cell elongation initiation.

plant biology↗

bioRxiv2025

Phosphoproteomics uncovers rapid and specific transition from plant two-component system signaling to Ser/Thr phosphorylation by the intracellular redox sensor AHK5

The Arabidopsis thaliana histidine kinase 5 (AHK5) is proposed to function as a intracellular sensor of active oxygen species (ROS) and redox conditions, fine-tuning responses to diverse ROS-inducing stimuli through a multistep phosphorelay (MSP) system. To elucidate the mechanism of ROS perception by AHK5 and signaling through posttranslational modifications, a comparative phosphoproteomics analysis was conducted using ahk5 loss-of-function and wild type seedlings in response to exogenously applied H2O2. Under control and H2O2-related conditions, a rapid signaling transition from the MSP to Ser/Thr phosphorylation was observed. AHK5 appears to regulate ROS-responsive phosphorylation at the plasma membrane by the modification of nanodomain components such as remorins, aquaporins, IQDs, and patellins, positioning it as a central integrator of redox signaling during adaptation to diverse stresses. AHK5 drives a distinct, ABA-independent signaling pathway for H2O2-induced stomatal closure, likely by regulating phosphorylation of key components such as RBOHD, CAS, and HPCA1. Moreover, AHK5-fine-tuned root development involves ABA-dependent signaling and appears to act through modulation of auxin transport via phosphorylation of auxin carrier, highlighting a mechanistic divergence between ROS responses in the shoot and root. Our data further suggest that AHK5 orchestrates stress-responsive nanodomain-associated signaling hubs through regulation of membrane trafficking, cytoskeletal dynamics, and endocytosis to mediate stress responses. HighlightAHK5 perceives and may amplify H2O2 signaling by linking two-component systems to Ser/Thr phosphorylation, likely by modulating membrane-associated signalosomes, thereby fine-tuning responses to stress-induced reactive oxygen species.

plant biology↗

bioRxiv2023

Cultural use of tropane alkaloids of Brugmansia species and cultivars in Colombia depends on local plant growth environment rather than genetic diversity

Borracheros or Angel Trumpets (Brugmansia spp.) of the Solanaceae plant family are known for producing scopolamine and other tropane alkaloids and are widely used by indigenous communities in the Andes for medicinal and ritual purposes. Growing different varieties has increased the popularity of Brugmansia species in recent years, leading to the promotion of hybridization to get new morphotypes. However, so far no medical or cultural use of plant extracts could be linked to selected Brugmansia species or cultivars. Moreover, until now there is only limited knowledge about the effect of hybridization on tropane alkaloid contents and/or diversity of Brugmansia species or cultivars. Here, a liquid chromatography-mass spectrometry (LC-MS) approach was applied to identify and characterize secondary metabolite contents in various Brugmansia species and hybrids from different geographic origins in Colombia. The analysis of the metabolic data sets revealed that tropane alkaloids and other secondary metabolites accumulate in a leaf and flower specific manner. Although some minor differences were found between Brugmansia subgroups, the only significant difference exists between plants collected in the Sibundoy Valley, where they have been domesticated by indigenous communities since a long time and those, which so far have not been used by humans at all. The different genetic constitutions of Brugmancia species and cultivars are not the dominating reason for their differences in tropane alkaloid contents and medical and cultural usages, as there is no clear taxonomical signature based on the metabolite properties for species segregation. Instead, their use by indigenous communities during ceremonies and for medical treatment such as wound healing, infection control, rheumatism and arthritis is rather caused by the plasticity of the individual plants to react to the local abiotic and biotic environments by the variation of secondary metabolite composition and by the differences in the bioavailability of the active compounds as result of the extraction method.

plant biology↗

bioRxiv2021

Integration of computational modeling and quantitative cell physiology reveals central parameters for the brassinosteroid-regulated elongation growth along the axis of the Arabidopsis root

Brassinosteroids (BR) are key hormonal regulators of plant development. However, whereas the individual components of BR perception and signaling are well characterized experimentally, the question of how they can act and whether they are sufficient to carry out the critical function of cellular elongation remains open. Here, we combined computational modeling with quantitative cell physiology to understand the dynamics of the plasma membrane (PM)-localized BR response pathway during the initiation of cellular responses in the epidermis of the Arabidopsis root tip that are be linked to cell elongation. The model, consisting of ordinary differential equations, comprises the BR induced hyperpolarization of the PM, the acidification of the apoplast and subsequent cell wall swelling. We demonstrate that the competence of the root epidermal cells for the BR response predominantly depends on the amount and activity of H+-ATPases in the PM. The model further predicts that an influx of cations is required to compensate for the shift of positive charges caused by the apoplastic acidification. A potassium channel was subsequently identified and experimentally characterized, fulfilling this function. Thus, we established the landscape of components and parameters for physiological processes potentially linked to cell elongation, a central process in plant development.

plant biology↗

bioRxiv2019

Quantum coherence in the photosynthesis apparatus of living cyanobacteria

The first step in photosynthesis is an extremely efficient energy transfer mechanism, which is difficult to be explained by classical short-range energy migration ("hopping") and led to the debate to which extent quantum coherence is involved in the energy transfer between the photosynthetic pigments. Embedding living cyanobacteria between the mirrors of an optical microresonator and using low intensity white light irradiation we observe vacuum Rabi splitting in the transmission and fluorescence spectra as a result of strong light matter coupling of the chlorophyll and the resonator modes. The Rabi-splitting scales with the number of chlorophyll a pigments involved in coherent coupling indicating forming a polaritonic state which is delocalized over the entire cyanobacterial thylakoid system, down to the single photon level. Our data provide evidence that a delocalized polaritonic state is the basis of the extremely high energy transfer efficiency under natural conditions.

biophysics↗